"We're seeing that the disparities occur as early as kindergarten and then remain and continue until the end of eighth grade," said Paul Morgan, who led the study at Pennsylvania State University in University Park.
"It's a consistent pattern of what we're interpreting as comparative underdiagnosis for minority populations," he told Reuters Health.
That's a concern, Morgan said, because it means some kids who could benefit from treatment - including medication or talk therapy - and extra help in the classroom may be missing out.
The researchers also found that compared to white children with the condition, minority kids who were diagnosed with ADHD were less likely to be prescribed medications, which include the stimulants Vyvanse, Ritalin and Concerta.
They tracked 15,100 kids from the kindergarten class of 1998-1999 using regular parent surveys.
Image: Latino child, via Shutterstock